1. Field of the Invention
The present invention is directed to a capillary, an interface and a holder for a capillary electrophoresis ("CE") system. In particular, the capillary, interface and holder are useful for planar capillary electrophoresis ("PCE") and related techniques.
2. Description of Related Art
A detailed description of PCE is provided in the article Glass Chips for High Speed Capillary Electrophoresis Separations With Submicrometer Plate Heights by Carlo S. Effenhauser, Andreas Manz and H. Michael Widmer, which was published in Analytical Chemistry, Volume 65, Oct. 1, 1993, pages 2637-2642, ("Glass Chips Article"), the contents of which are incorporated herein by reference.
CE and PCE are used in analytical and biomedical research for the rapid separation and analysis of charged species including synthetic polynucleotides, DNA sequencing fragments, DNA restriction fragments, amino acids, ions and the separation of proteins, viruses and bacteria.
CE and PCE typically utilize an electric potential difference to separate and transport components of a sample inside a capillary. A variety of detectors are available for detecting the sample components including uv-visible detection, electrochemical detection and more recently, laser induced fluorescence detection which involves labeling sample components with a fluorescent tag, such as e.g. fluorescein.
Laser induced fluorescence utilizes one or more lasers to illuminate a window section of the capillary. This illumination results in the laser excitation of the fluorescent material within the window section and causes the fluorescent material to emit radiation. These emissions are collected by a collection device and sent to a detector which converts the emission energy to a usable signal for analysis.
PCE utilizes a capillary defined by a network of interconnected, tiny, short channels formed in a planar housing. The network is useful for separating a sample into a small sample plug for testing or for combining or separating various reactants.
PCE has great potential since the small sample plug, used in combination with a short capillary and a high electrical potential allows for fast and efficient separation of the sample constituents with excellent resolution. Further, with PCE, multiple capillaries, each having multiple networks can be manufactured relatively inexpensively into the housing.
However, existing PCE systems are not entirely satisfactory since there is difficulty interfacing or connecting the network of tiny channels to electrical conductors and to samples, reactants or other fluids.
As provided in the Glass Chips Article, one way of interfacing each channel with an electrical conductor and reactant liquids includes drilling a port at the end of each channel. Next, a pipette tip is glued into the port and the pipette tip is filled with an ionic fluid. The electrical conductor is disposed in the ionic fluid.
This method of interfacing has numerous drawbacks. First, individually drilling each port in alignment with a channel and gluing each pipette tip into the port is relatively expensive. Second, a difference in hydrostatic pressure occurs if the height of the ionic fluid is not consistent in each of the pipette tips or the orientation of the housing is changed. The difference in hydrostatic pressure causes unwanted fluid flow in the channels. Thus, the level of fluid in each of the pipette tips must be carefully measured and maintained throughout the experiment to prevent unwanted fluid flow in the channels and the capillary housing must be maintained at the same orientation throughout the experiment.
Third, the test sample and reactants are in fluid communication with each other through the network of channels. Thus, the components can diffuse together and mix causing unwanted reactions or contamination between testing. This can be prevented by the inclusion of valves within the ports. However, this also increases the cost and complexity of the system.
Fourth, dead volumes can exist between the intersection of the pipette tip and the port which are difficult to clean. Thus, there is a risk of contamination and/or erroneous results if existing capillaries are reused.
Accordingly, there is a need for a capillary, an interface and a holder which (i) are relatively easy and inexpensive to manufacture, (ii) are relatively easy to use and clean, and (iii) reduce the potential for diffusion of the components between experiments.